µ-Oxo bridged diiron(III) complexes and hydrogen peroxide: oxygenation and catalase-like activities
The crystal structures of two dinuclear iron(III) compounds with a bent µ-oxo bridge, [Fe2O(CH3CO2)(tpa)2][ClO4]3· 2H2O and [Fe2O(CH3CO2)(mep)2][ClO4]3, were determined, where tpa and mep represent tris(2-pyridylmethyl)amine and N,N′-dimethyl-N,N′-bis(2-pyridylmethyl)ethane-1,2-diamine, respectively. Their structural features which include a (µ-oxo)(µ-acetato)diiron(III) core are very similar. In spite of this, these two complexes exhibit very different reactivity towards hydrogen peroxide in solution; the tpa complex showed high catalase-like activity, whereas that of the mep complex was negligible. In the oxygenation of cyclohexane the mep complex–H2O2 system exhibited high activity giving cyclohexanol and cyclohexanone, but formation of oxygenated products was negligible with the tpa complex–H2O2. The absorption spectrum of the tpa complex shows no change in the presence of H2O2; however a drastic change was observed in the spectrum of the mep complex on addition of H2O2. Based on the structural and spectroscopic data, the structures of the active species for catalase- and oxygenase-like functions and the origin of the differences in reactivity observed for these two compounds are discussed.